I was doing a bit of keyword research when I found something strange. Every single result came with the warning that it might harm my computer. These warnings are normal for warez and certain torrent sites, but I was getting warnings on searches for things like "men's fashion," where the top results were from reputable sites like Overstock and Amazon. A friend reported having similar problems.
I tried the site while logged in and logged out of a Google account without change. Disabling a few Firefox plugins seemed to not have an affect either.
My next step was to delete cookies from all but a handful of websites. And voila! my search results were back to normal. I've seen malware and strange things come through ad networks before, so I suspect that the root cause may lie in something coming through an adserver that attempts to redirect.
To the SMG readers, have you experienced a similar problem with Google results recently? Does clearing your cookies make a difference?
Could this be Microsoft's newest attempt to gain a larger slice of the search market? (I kid)
Update: Marissa Mayer explains that a human error at Google is to blame. I suppose my cookie paranoia coincided with the correction of the problem